1. Field of the Invention:
This invention relates to digital systems having a network of discrete hardware modules. More specifically, this invention relates to techniques for transmitting information such as status or interrupt signals within such networks.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art:
Many contemporary digital systems rely on a number of processors to perform complex, real-time applications. During the course of such real-time processing it is often necessary for one processor to interrupt or otherwise signal another processor. Specifically, each processor is typically programmed with a list of event occurrences (e.g. interrupt or error conditions) required to be communicated to other processors or hardware modules within the digital system.
At least two methods are commonly employed for communicating interrupt and event information among the processors and other modules within modern digital systems. In a first method the various components of the system are interconnected through a network of discrete interrupt lines. A separate line is required to transmit each event or interrupt signal from a particular module or processor to the remaining components within the system. Thus, sixteen separate interrupt lines would be required in a system having eight modules if each module were to provide a pair of interrupts to the others. In addition, each module would generally need to be outfitted with sixteen distinct input/output (I/O) ports. As a further example, a system having twelve modules--each disposed to generate five interrupt signals--would conventionally require sixty distinct interrupt lines. It is apparent that such an approach may result in systems burdened with a relatively large number of interrupt lines. Thus, a network of discrete interrupt lines may make large-scale systems relatively unwieldy and expensive.
In a second method, interrupt signals are conveyed on the system bus linking each of the modules within the network. In addition to transmitting interrupt messages, the bus is typically operative to transfer large quantities of data between modules in accordance with an established protocol. The interrupt messages must be designed to be compatible with this protocol. This may, in some instances, be extremely inconvenient. Moreover, the inclusion of interrupt messages on the bus reduces the available bus capacity to transfer data and other information between modules. Finally, the bus protocol may operate to delay unacceptably certain interrupt signals during periods of intense network activity.
Accordingly, a need in the art exists for a system to communicate signals among modules within a digital network without utilizing the system bus or a plurality of discrete interrupt lines.